KRAS and neoplasm: Four distinct MyoD-Cre transgenic genotypes were monitored for tumor incidence: K-Ras-wild type (WT) mice with floxed p53 allele/WT p53 allele or LSL-p53R172H allele/WT p53 allele (K-RasWTp53F/+ and K-RasWTp53R172H/+) and K-Ras-mutated mice with floxed p53 allele/WT p53 allele or LSL-p53R172H allele/WT p53 allele (K-RasG12Dp53F/+ and K-RasG12Dp53R172H/+) (Fig. 1A).